macOS: fix non control keys are not working for AppleScript

[bo2themax]

send key only works for control keys like enter currently; this adds (fixes) the support for other keys listed as available. Found by @paaloeye in #13180

The core of this fix is relying on UCKeyTranslate to get the corresponding character and code point from a key code using characters(byApplyingModifiers:). To reuse the existing code point check in ghosttyCharacters, I moved that into a separate function to avoid unexpected side effects.

Not sure which case could break if I just use characters(byApplyingModifiers:) regardlessly.

AI Disclosure

Claude wrote the unit tests and did some code review.

Tests seems flaky on ci, deleted it

[paaloeye]

Well done!

Tested it in my harness and it works as expected.

Test command: gtty surface broadcast --engine swift --offset -3..-1.
One would need four surfaces and Nushell installed.

[paaloeye]

I've been daily driving Ghostty with that — couldn't find any problems with it.
@bo2themax Is anything missing here? It wasn't trivial to discover using send key with anything other than enter, IMO it's worth updating the docs. I'm happy to give it go.